Home / Ask The Experts / If a person received a Tdap vaccine and then had a positive pertussis PCR two weeks later, could it be a false positive from the vaccine or should we consider this a case of pertussis? The patient had a cough, nausea, and vomiting for 2–3 days prior to PCR testing.

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If a person received a Tdap vaccine and then had a positive pertussis PCR two weeks later, could it be a false positive from the vaccine or should we consider this a case of pertussis? The patient had a cough, nausea, and vomiting for 2–3 days prior to PCR testing.

Recent Tdap vaccination does not affect PCR testing. PCR tests are used to detect DNA sequences of the Bordetella pertussis bacterium. PCR tests are very sensitive and could give a false positive result for other reasons. For more information on best practices when performing PCR testing for pertussis see www.cdc.gov/pertussis/php/pcr-bestpractices.

Last reviewed: October 31, 2023

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This page was updated on October 31, 2023.